Boilers have been used for generating steam in radiant heating systems in both residential and commercial applications for a number of years. The systems generally operate by heating boiler water to produce steam. The steam is then distributed through a piping system to distribute heat to the facility by having the distributed steam transfer heat to surrounding air. Once distributed, the resultant steam condenses and returns to the boiler to be heated again and redistributed.
Because of the way these boiler systems operate, it is necessary that there be sufficient water in the boiler system at all times. If the water level drops too low, the water in the boiler can flash to steam explosively, seriously injuring or killing people or damaging the boiler, facility or both. Steam boiler systems can also be damaged if they have too much water. In this case, liquid water can be forced from the boiler into the pipes along with the high-velocity steam which can lead to damage of piping, valves, or heating system components such as radiators. For these reasons, boiler systems are filled to their desired level during installation. They then include a Low Water Cutoff (LWCO) which will serve to turn off the heat source in the boiler if the water level drops below a safe level. The LWCO therefore serves as a protector against the system being operated with insufficient water and indicates that additional water needs to be added.
Historically, additional water was added manually to the boiler when the LWCO indicated a low water condition or boiler water levels were observed to be below normal operating levels. This was effective with sufficiently educated maintenance personnel in preventing overfilling. However, it was highly inconvenient and, if no one was around, could result in the boiler not providing heat until it was attended to. Therefore, recently, the water has been preferably added by mechanical or electronic water feed controllers.
Automatic water addition systems traditionally operated by adding water to the boiler until the LWCO no longer indicated a low water condition. At that time, the water level was presumed in a safe range and the heating source of the boiler could be enabled without risk of damage to the boiler. These systems, however, suffered from a series of problems.
The traditional role of the LWCO is to shut down boiler heat sources in the event that the water level is below a safe level, which is typically well below an optimum operating level. In addition to this function, the LWCO was configured to operate water feeding devices to replenish low water levels. The LWCO also serves to shut off the water feeding devices once the LWCO is satisfied by the water level. In particular, the LWCO was basically a switch that transferred power from the boiler's heating source to the automatic water feeder when a low water condition was detected and reversed the transfer once the low water condition was no longer detected. The system, therefore, automatically fed an amount of water into the boiler until the water level satisfied the LWCO. As it is a common practice for LWCO devices to be installed in such a manner that they operate slightly above the boiler's minimum safe water level, boiler systems that are automatically fed as noted above will be operating near at the boiler's minimum safe water level and generally no higher.
It is desirable in a boiler system to operate at a water level above the minimum safe water level for numerous reasons. First, operation above the minimum safe level provides an additional safety margin by adding hysteresis to the water level. Further, operating above the minimum safe level compensates for dynamic water levels due to boiling and surging of the boiler water. This prevents short-cycling of the boiler's burner due to the LWCO detecting these dynamic water levels caused by insufficient hysteresis in the water level. If the boiler is firing and it short-cycles due to these dynamic water levels, the burner controls are turned off in favor of the water feed. This cuts the heating cycle short and can cause flue gases to condense on internal boiler components. Over time, this reduces the life of heat exchangers and other critical components in the boiler and can lead to premature failures and costly repairs. When operating near the probe level of the LWCO, a slight leak, or even a fluctuation of the LWCO switch mechanism, can result in the burner being short-cycled unnecessarily.
Further, as a boiler system steams, water is converted to steam thereby lowering the water level of the boiler. This steam has a transit time as it passes through the heating system, condenses, and returns to the boiler as water. If the water level falls below the LWCO before the condensate returns to the boiler, the LWCO can detect a low water condition and initiate a water feed cycle. Depending on the delay in the condensate returning to the boiler, enough water may feed into the boiler that, when combined with the returned condensate, the boiler will be overfilled and flooded.
To deal with the problem of the water being prematurely fed due to the delay of returning condensate, delays have been added to some automatic water feeds so that the system's water level has a chance to stabilize before additional water is added. In particular, water is not added until a period of delay occurs after the LWCO was triggered. Therefore, the water was allowed to condense and return to the boiler so that the actual water level could be determined before water was added. This helped eliminate potential overfilling but can also result in increased short-cycling of the burner, when operating at the minimum water level.
To try and provide water above the minimum level in an automatic system, there are generally two possible methodologies for putting additional water into the boiler regardless of whether a delay after LWCO low water condition is used or not. In a simplistic case, water can be manually fed into the boiler system by a user pressing a manual feed button on the water feed controller essentially overriding the LWCO automatic feed to add more water. While this is effective, it requires a human user to operate the manual feed and to guess at how much water has been supplied (and needs to be supplied) to the boiler and provides little improvement over the original manual system.
In the alternative, the water feeder can be set to feed a fixed number of gallons into the boiler system each time the LWCO indicates a low water condition instead of simply filling until the LWCO no longer indicates a low water condition. When feeding a fixed number of gallons, it is required that the installer test the boiler system to identify precisely how much water a feed cycle must provide to prevent the feed cycle from accidentally overfilling the boiler. The water feeder must then be programmed to dispense that amount of water when the LWCO condition exists. The amount of water will be variable due to the water capacities of different models of boilers. An error in identifying the amount of water to be fed can lead to an insufficient amount of water, or too much water, being fed into the boiler. Insufficient water can lead to additional feed cycles being initiated by the water feeder, potentially overfilling and flooding the boiler. Similarly, if the amount of water that is programmed to be fed into the boiler is too large it is possible to overfill the boiler system. This flooding or overfilling of the boiler can prevent proper steam generation or result in water being propelled into the steam piping, damaging the piping systems.
In addition to the issues noted above, these systems still have further problems. If the boiler (or related components) was leaking, the continual water feeds would keep the water at a safe operating level, but would introduce a continual supply of fresh (oxygenated) water. This oxygenated water leads to increased corrosion in the boiler system and results in premature failure of the heating system.
All boilers will lose some water over time. The issue in determining whether water loss is significant enough to warrant replacement or repair requires examining how much additional water the system is requiring over a period of time (generally 30 days). As a leak will generally result in a steady loss, the only way to determine if a leak or other problem is sufficient to require action is to measure the amount of water added in a recent time period or to normalize loss to the calibration time period.
U.S. Pat. No. 6,688,329, the entire disclosure of which is herein incorporated by reference, is directed to one methodology for determining if excessive feed has been provided which could indicate that the boiler has a leak. The system described therein uses a display counter that indicates the number of gallons that the water feeder has dispensed since its totals were last reset. This display, therefore, provides water consumption information from which consumption over time can be computed.
This determination, however, requires extensive record keeping and manual computation. In particular, users must manually log the number of gallons shown on the display every 30 days so as to determine the 30 day usage rate. This is a complicated schedule to follow as it does not align with any calendar calculations and in most applications is impractical. In practice, users get the amount after some period, determine the length of the period, and normalize the amount of water used to a 30 day period. This number must then be manually compared against the manufacturer's expected water usage that must be found in water feeder or boiler documentation and can differ among boilers. This process is both manually cumbersome and fraught with the possibility of human error. Further, the process of normalization also introduces inaccuracies. In particular, as the period is not necessarily the same and water will be added as a batch when added, the normalization can serve to skew calculations such that the 30 day usage is too low or too high depending on whether fill actions occurred just outside, or just inside the measurement period.
Therefore, if the user does not record the water amounts from the display at reasonably consistent time intervals, the manual computation becomes more complicated and can become less accurate (as trends may not be as apparent or may end up averaged out over time). Further, the system relies on a person to correctly log usage data and to determine that excess usage is taking place. Therefore, the possibility of the introduction of human error is high and the indicators may not be reset or numbers may be recorded incorrectly. Further, if service personnel change, the new personnel may not know how or where the old data was recorded and may need to start essentially from zero.
There is still one additional problem with this methodology. Because the counter can be reset when the measurement is made, the measurements only occur at particular instances which are cyclical (generally with a minimum 30 days) and occur generally only once every time period. If the boiler developed a major leak soon after the water use for the prior 30-day period was recorded, the leak may cause significant damage before the next check (around 30 days later) would determine that a leak had even occurred. Further, with regards to smaller leaks, it could actually take three or more different measurement periods before a leak condition would become apparent to a user. This is because the fill activities generally will occur sporadically and an increase in the fill in the normalized period may not be recognized as a leak, but may instead simply be thought to be due to having an additional and expected fill event fall in the time between measurements.
In general, the existing practice of cyclical observation prohibits relatively real-time notification that excessive water use is taking place and can allow for error situations to be missed (or incorrectly detected) due to natural fluctuations within the periods of measurement.